This invention relates generally to a circuit breaker, and, more particularly, to a circuit breaker cassette assembly.
Circuit breakers are one of a variety of overcurrent protective devices used for circuit breaker protection and isolation. The basic function of a circuit breaker is to provide electrical system protection whenever an electrical abnormality occurs in any part of the system. In a rotary contact circuit breaker, current enters the system from a power line. The current passes through a load strap to a stationary contact fixed on the strap and then to a moveable contact. The moveable contact is fixedly attached to an arm, and the arm is mounted to a rotor that in turn is rotatably mounted in a cassette. As long as the fixed contacts are in physical contact with the moveable contacts, the current passes from the fixed contacts to the moveable contacts and out of the circuit breaker to downline electrical devices.
In the event of an overcurrent condition (e.g. a short circuit), extremely high electro-magnetic forces are generated. These electro-magnetic forces repel the movable contact away from the stationary contact. Because the moveable contact is fixedly attached to a rotating arm, the arm pivots and physically separates the stationary and moveable contacts, thus tripping the unit. When the contacts are rapidly opened as is the case during a trip caused by a short circuit event, an arc is produced. Swift extinction of the arc usually entails the resort to electromagnetic or pneumatic means for motivating the arc so as to increase its path length, promote removal of the arc from the breaker contacts, and facilitate cooling and splitting of the arc; all contributing to increasing the arc voltage to a value in excess of the system driving voltage. When the arc voltage surpasses the source voltage, it becomes difficult for the arc voltage to maintain the arc voltage so that the arc is extinguished. Accordingly, there occurs a voltage corresponding to the source voltage between the stationary contact and the moveable contact, thereby carrying out the circuit breaker operation. It is common practice to employ an arc chute assembly to extinguish this resultant arc.
Such arc chute assemblies consist of a plurality of metallic chute plates that are held in stacked, spaced-apart relationship by side panels that are fabricated from electrically non-conductive material. Retention of the chute plates between the side panels is usually achieved by providing the plates with small protrusions that are slipped into a series of radiused notches in the side panels.
Circuit breaker design, and more particularly, cassette design should enable the efficient and proper positioning of the various components, such as the rotor and arc chute assemblies, into the cassette. For example, improper installation of a rotor into a cassette can result in the two cassette half pieces not mating correctly together. Also, care must be taken to ensure that an arc chute assembly is correctly positioned into the cassette. This ensures proper rotation of the moveable contact arm as well as the proper spacing between the moveable contact and the plate closest to the moveable contact. Improper installation of either a rotor or an arc chute assembly into a cassette half piece will require disassembly and reassembly of the cassette. Such disassembly and reassembly is time consuming and can increase the production cost of the circuit breaker.